1. Field of the Invention
The present invention relates to a thermal activation device for heating an adhesive layer of a thermal activation sheet by a thermal head to thereby cause the thermal activation sheet to develop adhesiveness.
2. Description of the Related Art
Thermal activation labels are increasingly used as labels affixed to products manufactured and sold in processed food factories, supermarkets, etc. for indicating such information as product name, price, sellby date, etc. A thermal activation label includes an adhesive layer, which does not normally exhibit adhesiveness, the adhesive layer being activated when applied with a thermal energy, making it possible to affix the adhesive layer to a target object. Sheets having a similar adhesive layer, including the above thermal activation label, are herein referred to under the generic term “thermal activation sheet”.
As a conventional thermal activation device for activating such a thermal activation label, a device as disclosed in JP 11-79152 A has been put into practical use. This device includes a thermal head composed of a large number of heat generating elements arranged in one or multiple rows on a substrate. A thermal activation label is passed between the thermal head and a platen roller pressed against the thermal head to heat the thermal activation label, thereby activating an adhesive layer thereof. The use of such a thermal head provides such advantages as allowing a reduction in the overall size of the device as well as enabling a partial activation, whereby only an intended portion of the label can be activated.
In order to effect a clear separation between a thermal-activation portion and a non-thermal-activation portion when performing partial activation or the like in the thermal activation device, the heat generating elements must be able to effect heating and heat dissipation instantaneously. Further, in the case where the entire label surface is to be activated, to reliably activate the label up to its edge portion, it is necessary for the heat generating elements to be able to heat the thermal activation label to a fixed temperature or more instantaneously as the leading edge thereof approaches and reaches the position of the heat generating elements, and to effect heat dissipation instantaneously to lower the temperature of the thermal activation label to below the fixed temperature as the trailing edge thereof passes the position of the heat generating elements and the platen roller and thermal head come into direct contact with each other.
For this reason, conventional thermal activation devices employing a thermal head uses heat generating elements capable of outputting a large heat quantity to realize instantaneous heating. In addition, to realize instantaneous heat dissipation, a large radiator plate made of a material exhibiting high heat conductivity, such as aluminum, must be provided on the back surface of the thermal head. Therefore, the requisite power consumption and volume of the conventional thermal activation devices are large.